Attempts have begun in recent years to use microfluidic devices to analyze the components of fluids containing trace amounts of DNA, biological substances and so forth in various fields including medical diagnostics and biochemical testing.
Microfluidic devices are also referred to as microfluid devices, microfabricated devices, lab-on-a-chip and micro total analytical systems (μ-TAS), and are capable of accelerating reactions and analyses, reducing the amounts of required reagents and reducing waste products by carrying out reactions and analyses in minute, capillary channels contained within the device.
In the case of using such microfluidic devices to react with a sample in a fluid by fixing an enzyme, catalyst or functional group and so forth on the inside surface of a channel, or in the case of detecting DNA and so forth in a sample by fixing a probe such as a DNA fragment of a specific sequence, it is important to fix larger amounts of enzyme, catalyst or DNA fragments or other probes in order to improve reaction rate and analysis sensitivity.
The inside of the channel is preferably made to be porous in order to increase the fixed amount of a functional group, (bio)chemical substance or biological substance as described above in a channel. A known example of a channel in which a porous body is formed inside is that in which the entire inside of the channel is a porous body, and is formed by a method in which a silicon or aluminum sheet is made to be porous by etching and heat treatment within a range to a fixed depth from the surface of the sheet, followed by adhering a cover onto said porous surface (see Japanese Unexamined Patent Application, First Publication No. H6-169756). However, since the entire inside of this channel is porous, and the fluid that flows through this channel flows through the pores of said porous body, a high pressure of several hundred Kpa is required for the fluid to flow at an adequate flow rate through the channel. Consequently, the microfluidic device body and connecting ports for introducing the fluid were required to be of a rugged structure capable of withstanding high pressure. In addition, since the fixation density of these inorganic materials is small in addition to the types of functional groups introduced onto the surface being limited, they still ended up being inadequate even if a porous body was employed. Moreover, since silicon and metal are optically opaque, thereby preventing pigments and fluorescent pigments fixed to the inside of the porous body from being observed from the outside, they did not contribute to improvement of the sensitivity of light absorption or fluorescent detection. Since these materials are optically opaque, there is a large amount of scattering of excitation light during fluorescence measurement, and since excitation light unable to be completely cut out with a filter ends up entering the receiving side, the baseline of measured fluorescent intensity becomes higher, thereby inviting a decrease in the S/N ratio and a decrease in reliability. Moreover, since silicon and metal have high thermal conductivity, it is difficult to provide a temperature gradient in a channel, thereby placing limitations on use as a microfluidic device.
On the other hand, since resins (organic polymers) have numerous types of functional groups that can be introduced onto their surface, and the fixation densities of those functional groups are high, they are preferable for use as constituent materials of the inner surface of the channels of microfluidic devices (see Japanese Unexamined Patent Application, First Publication No. 2000-2705). However, in processes involving the formation of a grooved channel like that known as a production process of a resin microfluidic device (see, for example, Japanese Unexamined Patent Application, First Publication No. 2000-46797), although a process is described in which a grooved channel having minute surface irregularities on the bottom is formed by forming minute surface irregularities on the surface of a base material by electron etching, coating an activating energy beam-curable compound thereon, radiating an energy beam onto those portions other than the channel to cure the activating energy beam-curable compound, and removing the uncured activating energy beam-curable compound of the non-irradiated portion, since this only involves the providing of surface irregularities for imparting hydrophilicity to the channel bottom of said microfluidic device, a three-dimensional mesh-like porous layer is not formed. Although it is not known whether or not more probe is fixed by this microfluidic device having an inner surface with surface irregularities than by a microfluidic device in which the inner surface is not treated, according to a confirmatory experiment conducted by the inventors of the present invention, the degree of the increase was small and was not considered to be adequate.
On the other hand, a method of increasing the fixed amount of an enzyme or catalyst on the surface of a sheet and so forth instead of the surface of a channel is disclosed in which a thin porous layer is formed on the surface of said sheet followed by fixing the enzyme or catalyst thereon (see Japanese Unexamined Patent Application, First Publication No. 2000-2705). However, a method in which such a porous layer is provided on one side of the inner surface of a minute channel of a microfluidic device has heretofore not been known.
In addition, a method of producing a hydrophilic porous membrane is disclosed in which a mixed solution of an energy beam-curable resin, linear polymer and solvent is coated onto a base material and irradiated with energy followed by contacting with a non-solvent of the linear polymer to cause phase separation (see Japanese Unexamined Patent Application, First Publication No. 10-007,835). However, with respect to this method as well, a method of providing such a resin at a uniform thickness on the inner surface of a minute channel of a microfluidic device has heretofore not been known.
The objects to be solved by the present invention consist of providing a microfluidic device, in which a porous resin layer having a three-dimensional mesh structure, which is capable of optimally fixing a large amount of enzyme, antigen or other protein or catalyst on the inner surface of a minute channel of a microfluidic device without obstructing the channel of the microfluidic device, is formed at a uniform thickness on the surface of said channel, a microfluidic device in which said porous resin layer is formed at an arbitrary location in the direction of flow of the channel, a microfluidic device in which said porous resin layer is formed on a portion of the cross-section of the channel, and a production process of said microfluidic device.